Electrode for solid-state batteries and solid-state battery

ABSTRACT

An electrode for solid-state batteries, comprising a PTC resistor layer, and a solid-state battery comprising the electrode. The electrode may be an electrode for solid-state batteries, wherein the electrode comprises an electrode active material layer, a current collector and a PTC resistor layer disposed between the electrode active material layer and the current collector; wherein the PTC resistor layer contains an electroconductive material, an insulating inorganic substance and a polymer; and wherein a porosity of the PTC resistor layer is from 5% to 13%.

TECHNICAL FIELD

The disclosure relates to an electrode for solid-state batteries and asolid-state battery comprising the electrode.

BACKGROUND

In a battery used as an in-vehicle power source or as a power source fornotebook PCs and portable devices, the temperature of the whole batterymay increase due to an internal short circuit or overcharging and mayhave adverse effects on the battery itself or on a device using thebattery.

As a measure to prevent the adverse effects, a technique of using anelectrode has been attempted, the electrode comprising a positivetemperature coefficient (PTC) resistor layer which has electronconductivity at room temperature and which shows an increase inelectronic resistance value with an increase in temperature.

Patent Literature 1 discloses an all-solid-state state batterycomprising a laminate of a cathode active material layer, a solidelectrolyte layer, and an anode active material layer in this order, anda restraining member that applies a restraining pressure to the laminatein a laminated direction, wherein a PTC layer containing a conductivematerial, an insulating inorganic substance and a polymer, is disposedat least at one of a position between the cathode active material layerand a cathode current collecting layer for collecting electrons of thecathode active material layer, and a position between the anode activematerial layer and an anode current collecting layer for collectingelectrons of the anode active material layer, and the content of theinsulating inorganic substance in the PTC layer is 50 volume % or more.

Patent Literature 2 discloses an all-solid-state battery comprising: acathode layer comprising a cathode active material layer and a cathodecurrent collector; an anode layer comprising an anode active materiallayer and an anode current collector; and a solid electrolyte layerdisposed between the cathode active material layer and the anode activematerial layer, wherein the all-solid-state battery further comprises aPTC film between the cathode current collector and the cathode activematerial layer and/or between the anode current collector and the anodeactive material layer, and the PTC film contains a conductive materialand a resin.

-   Patent Literature 1: Japanese Patent Application Laid-Open (JP-A)    No. 2018-014286-   Patent Literature 2: JP-A No. 2017-130283

However, the electrode as disclosed in Patent Literature 1, theelectrode comprising the PTC resistor layer containing the insulatinginorganic substance, has a problem in that electronic resistance at theinterface between the PTC resistor layer and the electrode activematerial layer in a room temperature condition (15° C. to 30° C.) islarge. The electrode as disclosed in Patent Literature 2, the electrodecomprising the PTC resistor layer not containing the insulatinginorganic substance, has a problem in that electronic resistance isdecreased in a high temperature condition due to the effects ofconfining pressure.

SUMMARY

The disclosed embodiments were achieved in light of the abovecircumstance. An object of the disclosed embodiments is to provide anelectrode for solid-state batteries, comprising at least a PTC resistorlayer in which electronic resistance in a room temperature condition islow. Another object of the disclosed embodiments is to provide asolid-state battery comprising the electrode.

In a first embodiment, there is provided an electrode for solid-statebatteries, wherein the electrode comprises an electrode active materiallayer, a current collector and a PTC resistor layer disposed between theelectrode active material layer and the current collector; wherein thePTC resistor layer contains an electroconductive material, an insulatinginorganic substance and a polymer; and wherein a porosity of the PTCresistor layer is from 5% to 13%.

The insulating inorganic substance may be a metal oxide.

The electroconductive material may be carbon black.

In another embodiment, there is provided a solid-state batterycomprising a cathode, an anode and an electrolyte layer disposed betweenthe cathode and the anode, wherein at least one of the cathode and theanode is the above-mentioned electrode for solid-state batteries.

For the electrode for solid-state batteries according to the disclosedembodiments, the porosity of the PTC resistor layer is in the specificvalue range, whereby more electron-conductive paths than ever before arecontained inside the PTC resistor layer, and excellent electronconductivity inside the PTC resistor layer is obtained. As a result,when the electrode is used in a solid-state battery, an increase in theelectronic resistance inside the PTC resistor layer can be suppressed,and a decrease in the performance of the solid-state battery can besuppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings,

FIG. 1 is a view showing an example of the layer structure of theelectrode for solid-state batteries according to the disclosedembodiments, and it is also a schematic cross sectional view of theelectrode along the laminating direction;

FIG. 2 is a view showing an example of the layer structure of thesolid-state battery of the disclosed embodiments, and it is also aschematic cross sectional view of the solid-state battery along thelaminating direction;

FIG. 3 is a schematic view of a circuit for electronic resistancemeasurement, which includes an evaluation sample; and

FIG. 4 is a view showing a relationship between the electronicresistance of an evaluation sample of an electrode and the resistance ofa solid-state battery comprising the electrode.

DETAILED DESCRIPTION 1. Electrode for Solid-State Batteries

The electrode for solid-state batteries according to the disclosedembodiments is an electrode for solid-state batteries, wherein theelectrode comprises an electrode active material layer, a currentcollector and a PTC resistor layer disposed between the electrode activematerial layer and the current collector; wherein the PTC resistor layercontains an electroconductive material, an insulating inorganicsubstance and a polymer; and wherein a porosity of the PTC resistorlayer is from 5% to 13%.

It is known that if a layer containing an electroconductive material anda polymer is disposed between the electrode active material layer andthe current collector, the layer shows a PTC resistor function (a rapidincrease in electronic resistance) when the temperature of the layerexceeds the melting point of the polymer by heating. The PTC resistorfunction is exerted when the particles of the electroconductivematerial, which are in contact with each other, are separated by thermalexpansion of the polymer and result in blocking of electron conduction.In the disclosed embodiments, the layer showing such a PTC resistorfunction is referred to as “PTC resistor layer”.

In the solid-state battery comprising the PTC resistor layer, when thetemperature of the solid-state battery is increased due to overchargingor a short circuit, electron conduction between the electrode activematerial layer and the current collector is blocked, and anelectrochemical reaction is arrested. Accordingly, a further increase intemperature is suppressed and makes it possible to prevent adverseeffects on the solid-state battery itself and on a device using thesolid-state battery.

For the PTC resistor layer containing the electroconductive material andthe polymer, the polymer is deformed and fluidized when pressure isapplied to the solid-state battery, whereby the PTC resistor layercannot maintain its structure and, as a result, may fail to exert thePTC resistor function. In Patent Literature 1, for the purpose ofallowing the PTC resistor layer to maintain its structure even whenpressure is applied to the solid-state battery, the PTC resistor layerthat further contains an insulating inorganic substance, which isgenerally said to have high strength, is disclosed. It was thought thatinside the PTC resistor layer, electronic resistance is increased by theinsulating inorganic substance, thereby increasing electronic resistancein the whole electrode.

However, as a result of research, it was found that in the electrodecomprising the PTC resistor layer containing the insulating inorganicsubstance, the electronic resistance inside the PTC resistor layer ishigher than expected. This seems to be because, since the PTC resistorlayer contains the insulating inorganic substance, many pores arepresent inside the PTC resistor layer.

For the electrode for solid-state batteries according to the disclosedembodiments, the porosity of the PTC resistor layer is in the specificvalue range, whereby when the electrode is used in a solid-statebattery, a decrease in the performance of the solid-state battery can besuppressed.

The electrode for solid-state batteries according to the disclosedembodiments comprises an electrode active material layer, a currentcollector and a PTC resistor layer.

FIG. 1 is a view showing an example of the layer structure of theelectrode for solid-state batteries according to the disclosedembodiments, and it is also a schematic cross sectional view of theelectrode along the laminating direction. As shown in FIG. 1, anelectrode 10 for solid-state batteries according to the disclosedembodiments, comprises an electrode active material layer 2, a currentcollector 3, and a PTC resistor layer 1 disposed between the electrodeactive material layer 2 and the current collector 3.

Hereinafter, these layers of the electrode for solid-state batterieswill be described in detail.

(1) PTC Resistor Layer

The PTC resistor layer is a layer which contains an electroconductivematerial, an insulating inorganic substance and a polymer, and which isdisposed between the electrode active material layer and the currentcollector.

The electroconductive material contained in the PTC resistor layer isnot particularly limited, as long as it has electroconductivity. As theelectroconductive material, examples include, but are not limited to,carbon-containing electroconductive materials such as carbon black,activated carbon, carbon fiber (e.g., carbon nanotube, carbon nanofiber)and graphite. The electroconductive material contained in the PTCresistor layer may be carbon black. The electroconductive material maybe in a particulate form. As the particulate form, examples include, butare not limited to, a fibrous form.

The volume ratio of the electroconductive material in the PTC resistorlayer is not particularly limited. When the total volume of theelectroconductive material, the insulating inorganic substance and thepolymer is determined as 100 volume %, the volume ratio of theelectroconductive material in the PTC resistor layer may be from 7volume % to 50 volume %, or it may be from 7 volume % to 10 volume %.

The insulating inorganic substance contained in the PTC resistor layerfunctions to suppress deformation and fluidization of the PTC resistorlayer in the electrode for solid-state batteries, both of which are dueto high temperature and pressure.

The insulating inorganic substance is not particularly limited, as longas it is a material that has a higher melting point than thebelow-described polymer. As the insulating inorganic substance, examplesinclude, but are not limited to, a metal oxide and a metal nitride. Asthe metal oxide, examples include, but are not limited to, alumina,zirconia and silica. As the metal nitride, examples include, but are notlimited to, a silicon nitride. Also, as the insulating inorganicsubstance, examples include, but are not limited to, a ceramic material.The insulating inorganic substance may be a metal oxide.

In general, the insulating inorganic substance is in a particulate form.The insulating inorganic substance may be primary particles or secondaryparticles.

The average particle diameter (D₅₀) of the insulating inorganicsubstance may be from 0.2 μm to 5 μm, or it may be from 0.4 μm to 2 μm,for example. The distribution of the insulating inorganic substanceparticles is not particularly limited. The distribution of the particlesmay be a normal distribution when it is represented by a frequencydistribution.

The volume ratio of the insulating inorganic substance in the PTCresistor layer is not particularly limited. When the total volume of theelectroconductive material, the insulating inorganic substance and thepolymer is determined as 100 volume %, the volume ratio of theinsulating inorganic substance in the PTC resistor layer may be from 40volume % to 85 volume %, or it may be from 50 volume % to 60 volume %.

When the volume ratio of the insulating inorganic substance in the PTCresistor layer is too small, it may be difficult to sufficientlysuppress the deformation and fluidization of the PTC resistor layer,both of which are due to heating and pressure. On the other hand, whenthe volume ratio of the insulating inorganic substance in the PTCresistor layer is too large, the volume ratio of the polymer isrelatively small. As a result, the effect of separating the particles ofthe electroconductive material by the polymer may be insufficientlyexerted, and an increase in electronic resistance may be insufficient.Also when the volume ratio of the insulating inorganic substance in thePTC resistor layer is too large, electroconductive paths, which areformed by the electroconductive material, may be blocked by theinsulating inorganic substance, and the electron conductivity of the PTCresistor layer during normal use may decrease. In the disclosedembodiments, the electron conductivity of the PTC resistor layer meansthe property of conducting electrons through the PTC resistor layer, andit is strictly different from the electroconductivity of the PTCresistor layer (the property of conducting electricity through the PTCresistor layer).

The porosity of the PTC resistor layer is generally from 5% to 13%. Itmay be from 5% to 12%, or it may be from 5% to 11%.

As will be shown below in Comparative Example 1, for a conventionalsolid-state battery, the porosity of the PTC resistor layer was morethan 30%. In the disclosed embodiments, by using the PTC resistor layerhaving a porosity which is smaller than ever before and which is in thespecific value range, the electron conductivity of the PTC resistorlayer is increased higher than ever before. It is presumed that this isbecause, for the PTC resistor layer having a higher density than everbefore, the number of the electron-conductive paths inside the layer islarger than ever before.

Accordingly, by using the PTC resistor layer having such excellentelectron conductivity, a decrease in the performance of the solid-statebattery can be suppressed.

When the porosity is more than 13%, the number of theelectron-conductive paths inside the PTC resistor layer is too small.Accordingly, the electron conductivity of the PTC resistor layerdeteriorates. On the other hand, it is possible to produce the PTCresistor layer having a porosity of less than 5%. However, it is noteasy due to the following reason. At least three different materials(the electroconductive material, the insulating inorganic substance andthe polymer) are needed to form the PTC resistor layer. Even if thematerials are mixed as well as possible by use of a solvent, etc., it isdifficult to prepare an absolutely uniform mixture, and it is inevitableto avoid pore formation in the dried PTC resistor layer.

The porosity of the PTC resistor layer can be controlled to 5% to 13% bya pressing method such as roll pressing (which will be described below),cold isostatic pressing (CIP) and hot isostatic pressing (HIP).

In general, it is often difficult to control the porosity of the PTCresistor layer to 5% to 13% by confining the solid-state battery withthe below-described confining member. This is because the pressureapplied by the confining member to the solid-state battery is onlyenough to closely attach the layers constituting the solid-statebattery, and the pressure is not enough to change the internal structureof the PTC resistor layer and to reduce the pores inside the layer. Alsofor the conventional solid-state battery, the porosity of the PTCresistor layer is more than 30% (see Comparative Example 1).

Accordingly, even if the conventional solid-state battery is combinedwith the confining member, it is inconceivable that the porosity of thePTC resistor layer is decreased to 5% to 13%.

Also, the porosity of the PTC resistor layer can be controlled to 5% to13% by methods other than the pressing method, such as drying underreduced pressure and heating.

In the case of forming the PTC resistor layer through one-timeapplication of the slurry, the method for calculating the porosity is asfollows. First, for the laminate of the PTC resistor layer and thecurrent collector (hereinafter, the laminate may be referred to as“laminate A”) and for a current collector that is the same type as thecurrent collector used to produce the laminate A, the mass and thethickness are measured as follows.

The mass is measured by the following method.

First, the laminate A and the current collector are each cut into anarea of 1 cm². The mass M₁ of the cut laminate A and the mass M₀ of thecut current collector are measured by use of an analytical balance(product name: GR-202, manufactured by: A&D Co., Ltd.)

The thickness is measured by the following method.

The thickness T₁ of the cut laminate A and the thickness T₀ of the cutcurrent collector are measured by use of a thickness gauge (productname: PG-01J, manufactured by: Teclock Corporation, probe: ZS-579).

Next, the density of the PTC resistor layer is calculated by thefollowing method.

The density D (g/cm³) of the PTC resistor layer is obtained by thefollowing formula (X), using the true densities (g/cm³) of the materialsused to form the PTC resistor layer (that is, the electroconductivematerial, the insulating inorganic substance and the polymer) and thevolume ratios (%) of the materials in the PTC resistor layer.D=(TD ₁ ×V ₁ +TD ₂ ×V ₂ TD ₃ ×V ₃)/100  Formula (X)where D is the density (g/cm³) of the PTC resistor layer; TD₁ is thetrue density (g/cm³) of the electroconductive material; V₁ is the volumeratio (%) of the electroconductive material; TD₂ is the true density(g/cm³) of the insulating inorganic substance; V₂ is the volume ratio(%) of the insulating inorganic substance; TD₃ is the true density(g/cm³) of the polymer; and V₃ is the volume ratio (%) of the polymer.

The porosity P (%) of the PTC resistor layer is calculated by thefollowing formula (Y), using the above-described thickness, mass anddensity values.P=[(M ₁ −M ₀)/{(T ₁ −T ₀)×1 cm² ×D}]×100  Formula (Y)where P is the porosity (%) of the PTC resistor layer; M₁ is the mass(g) of the laminate A; M₀ is the mass (g) of the current collector; T₁is the thickness (cm) of the laminate A; T₀ is the thickness (cm) of thecurrent collector; and D is the density (g/cm³) of the PTC resistorlayer.

In the case of forming the PTC resistor layer through, like thebelow-described modified example of forming the PTC resistor layer,two-time application of the slurry, first, the porosities of thebelow-described first and second coating layers are calculated. Then,the weighted average of the two porosities is calculated, and thethus-obtained value is determined as the porosity of the PTC resistorlayer.

The detailed method for calculating the porosity is as follows.

For the laminate A (the laminate of the PTC resistor layer formed bytwo-time application of the slurry and the current collector), for alaminate obtained by one-time application of the slurry to a surface ofthe current collector (hereinafter, the laminate may be referred to as“laminate a”) and for the current collector that is the same type as theone used to produce the laminate A, the mass and the thickness aremeasured. The method for measuring the mass and the method for measuringthe thickness are the same as the above-described methods using theanalytical balance and the thickness gauge.

The method for calculating the density of each layer formed by slurryapplication, follows the formula (X). In this case, the variables (TD₁,V₁, TD₂, V₂, TD₃ and V₃) of the formula (X) are obtained from thecomponents and composition of each slurry. Hereinafter, the density ofthe first coating layer and that of the second coating layer are definedad D¹ and D², respectively.

The porosity P¹ (%) of the first coating layer is calculated by thefollowing formula (Y1), using the above-described thickness, mass anddensity values.P ¹=[(M ₂ −M ₀)/{(T ₂ −T ₀)×1 cm² ×D ¹}]×100  Formula (Y1)where P¹ is the porosity (%) of the first coating layer; M₂ is the mass(g) of the laminate a; M₀ is the mass (g) of the current collector; T₂is the thickness (cm) of the laminate a; T₀ is the thickness (cm) of thecurrent collector; and D¹ is the density (g/cm³) of the first coatinglayer.

The porosity P² (%) of the second coating layer is calculated by thefollowing formula (Y2), using the above-described thickness, mass anddensity values.P ²=[(M ₁ −M ₂)/{(T ₁ −T ₂)×1 cm² ×D ²}]×100  Formula (Y2)where P² is the porosity (%) of the second coating layer; M₁ is the mass(g) of the laminate A; M₂ is the mass (g) of the laminate a; T₁ is thethickness (cm) of the laminate A; T₂ is the thickness (cm) of thelaminate a; and D² is the density (g/cm³) of the second coating layer.

The weighted average of the above-described two porosities is calculatedby the following formula (Y3), and the thus-obtained value (P) isdetermined as the porosity of the PTC resistor layer.P=(P ¹×(T ₂ −T ₀)+P ²×(T ₁ −T ₂))/(T ₁ −T ₀)  Formula (Y3)where P is the porosity (%) of the PTC resistor layer; P¹ is theporosity (%) of the first coating layer; T₂ is the thickness (cm) of thelaminate a; T₀ is the thickness (cm) of the current collector; P² is theporosity (%) of the second coating layer; and T₁ is the thickness (cm)of the laminate A.

Even in the case of forming the PTC resistor layer through three-timeapplication of the slurry, the porosity of the PTC resistor layer can beobtained in the same manner as the case of forming the PTC resistorlayer through two-time application of the slurry. More specifically, theporosities of the layers formed by the slurry application arecalculated, and the weighted average is determined as the porosity ofthe PTC resistor layer.

Also, the porosity of the PTC resistor layer can be measured from thesolid-state battery thus formed or from the electrode taken outtherefrom. In this case, as the measuring method, examples include, butare not limited to, image analysis.

As the method for measuring the porosity by image analysis, examplesinclude, but are not limited to, the following method: a cross sectionof the electrode containing the PTC resistor layer or a cross section ofthe PTC resistor layer itself is processed by, for example, a crosssection polisher (CP) and/or focused ion beam (FIB); a scanning electronmicroscopy image (SEM image) of the cross section is taken; and theporosity is measured from the image. In the case of calculating theporosity from the cross section of the electrode, the thickness of thePTC resistor layer is determined as the distance between the electrodeactive material layer and the current collector.

The polymer contained in the PTC resistor layer is not particularlylimited, as long as it is a polymer that expands when its temperatureexceeds its melting point by heating. As the polymer, examples include,but are not limited to, thermoplastic resins such as polypropylene,polyethylene, polyvinyl chloride, polyvinylidene fluoride (PVDF),polyfluoroethylene, polystyrene, ABS resin, methacryl resin, polyamide,polyester, polycarbonate and polyacetal. These polymers may be usedalone or in combination of two or more kinds.

From the viewpoint of melting point and ease of processing, the polymermay be a fluorine-containing polymer such as polyvinylidene fluoride andpolyfluoroethylene, or it may be polyethylene. The polymer may bepolyvinylidene fluoride.

The volume ratio of the polymer in the PTC resistor layer is notparticularly limited. When the total volume of the electroconductivematerial, the insulating inorganic substance and the polymer isdetermined as 100 volume %, the volume ratio of the polymer in the PTCresistor layer may be from 8 volume % to 60 volume %, or it may be from8 volume % to 45 volume %.

The thickness of the PTC resistor layer is not particularly limited. Itmay be from about 1 μm to about 30 μm.

(2) Electrode Active Material Layer

The electrode active material layer is not particularly limited, as longas it contains at least an electrode active material. As needed, it maycontain a binder, an electroconductive material, and a solidelectrolyte.

In the case of using the electrode for solid-state batteries accordingto the disclosed embodiments as the cathode, the electrode activematerial is not particularly limited, as long as it is an electrodeactive material that is generally used as a cathode active material. Forexample, when transferred ions are lithium ions, as the cathode activematerial, examples include, but are not limited to, a compound having alayered structure (such as LiCoO₂ and LiNiO₂), a compound having aspinel-type structure (such as LiMn₂O₄), and a compound having anolivine-type structure (such as LiFePo₄).

In the case of using the electrode for solid-state batteries accordingto the disclosed embodiments as the anode, the electrode active materialis not particularly limited, as long as it is an electrode activematerial that is generally used as an anode active material. Forexample, when the transferred ions are lithium ions, as the anode activematerial, examples include, but are not limited to, a carbonaceousmaterial, a lithium alloy, an oxide and a nitride.

The binder is not particularly limited, as long as it is chemically andelectrically stable. As the binder, examples include, but are notlimited to, a fluorine-containing binder such as polyvinylidene fluoride(PVDF) and polytetrafluoroethylene (PTFE).

The electroconductive material is not particularly limited, as long asit has electroconductivity. As the electroconductive material, examplesinclude, but are not limited to, carbonaceous materials such as carbonblack, activated carbon, carbon fiber (e.g., carbon nanotube, carbonnanofiber) and graphite.

The material for the solid electrolyte is not particularly limited, aslong as it has ion conductivity. As the material, examples include, butare not limited to, inorganic materials such as a sulfide material andan oxide material. As the sulfide material, examples include, but arenot limited to, Li₂S—SiS₂, LiI—Li₂S—SiS₂, LiI—Li₂S—P₂S₅,LiI—Li₂O—Li₂S—P₂S₅, LiI—Li₂S—P₂O₅, LiI—Li₃PO₄—P₂S₅, Li₂S—P₂S₅, Li₃PS₄,LiI—LiBr—Li₂S—P₂S₅ and Li₂S—P₂S₅—GeS₂.

(3) Current Collector

The material for the current collector is not particularly limited, aslong as it has electron conductivity. As the material for the currentcollector, examples include, but are not limited to, Al, Cu, Ni, SUS andFe. In the case of using the electrode for solid-state batteriesaccording to the disclosed embodiments as the cathode, Al may be used asthe material for the current collector. In the case of using theelectrode for solid-state batteries according to the disclosedembodiments as the anode, Cu may be used as the material for the currentcollector.

(4) Method for Producing the Electrode for Solid-State Batteries

The method for producing the electrode for solid-state batteries is notparticularly limited, as long as the above-described electrode forsolid-state batteries can be obtained by the method. Hereinafter, twoembodiments of the method for producing the electrode for solid-statebatteries will be described. The method for producing the electrode forsolid-state batteries according to the disclosed embodiments, is notlimited to the two embodiments.

A. First Embodiment

The first embodiment of the method for producing the electrode forsolid-state batteries comprises (a) forming the PTC resistor layer onone surface of the current collector and (b) laminating the electrodeactive material layer on the PTC resistor layer.

(a) Forming the PTC Resistor Layer on One Surface of the CurrentCollector

This is a step of forming the PTC resistor layer by applying the firstslurry to one surface of the current collector and drying the appliedfirst slurry.

The first slurry contains an electroconductive material, an insulatinginorganic substance and a polymer. Details of the materials are asdescribed above. The content ratio of the electroconductive material,the insulating inorganic substance and the polymer in the first slurryand in the below-described second slurry, may be appropriatelydetermined so as to correspond to the volume ratio and distribution ofthe electroconductive material, the insulating inorganic substance andthe polymer in the PTC resistor layer of the electrode for solid-statebatteries.

For the content ratio of the materials in the first slurry, theelectroconductive material, the polymer and the insulating inorganicsubstance may be at a volume ratio of 10:30:60, for example.

The first slurry may contain a non-aqueous solvent for dissolving ordispersing the electroconductive material, the insulating inorganicsubstance and the polymer. The type of the non-aqueous solvent is notparticularly limited. As the non-aqueous solvent, examples include, butare not limited to, N-methylpyrrolidone, acetone, methyl ethyl ketoneand dimethylacetamide. From the viewpoint of safety such as high flashpoint, small influence on human body and so on, the non-aqueous solventmay be N-methylpyrrolidone.

The content ratio of the non-aqueous solvent in the first slurry is notparticularly limited. When the total volume of the first slurry isdetermined as 100 volume %, the non-aqueous solvent may be from 80volume % to 93 volume %, or it may be from 82 volume % to 90 volume %.

The method for forming the PTC resistor layer is not particularlylimited. Hereinafter, a typical example and a modified example of themethod for forming the PTC resistor layer, will be described. However,the method for forming the PTC resistor layer is not limited to the twoexamples.

In the typical example of the method for forming the PTC resistor layer,the first slurry in which the electroconductive material, the insulatinginorganic substance and the polymer are dispersed in the non-aqueoussolvent, is applied onto the current collector, and the applied slurryis dried. To uniformly form the PTC resistor layer, the solid contentconcentration of the first slurry containing the electroconductivematerial, the insulating inorganic substance and the polymer, may befrom 13 mass % to 40 mass %.

The thickness of the PTC resistor layer is not particularly limited. Itmay be from about 1 μm to about 30 μm.

The condition for drying the first slurry is not particularly limited.For example, it may be a temperature condition in which the non-aqueoussolvent can be distilled away.

In the modified example of the method for forming the PTC resistorlayer, the PTC resistor layer is formed by further applying the secondslurry to the surface of the layer formed by use of the first slurry(hereinafter, it may be referred to as “first coating layer”). In thiscase, the PTC resistor layer is a layer comprising the solid content ofthe second slurry and the first coating layer.

The second slurry contains an electroconductive material and a polymer.The second slurry may further contain an insulating inorganic substance.When the insulating inorganic substance is not contained in the secondslurry, contact between the PTC resistor layer and the electrode activematerial layer can be better compared to the case where the secondslurry contains the insulating inorganic substance.

For the content ratio of the materials in the second slurry, in the casewhere the insulating inorganic substance is not contained in the secondslurry, the electroconductive material and the polymer may be at avolume ratio of from 85:15 to 20:80, for example.

The content ratio of the non-aqueous solvent in the second slurry is notparticularly limited. When the total volume of the second slurry isdetermined as 100 volume %, the non-aqueous solvent may be from 75volume % to 95 volume %, or it may be from 85 volume % to 90 volume %.

The method for applying and drying the second slurry is not particularlylimited. In general, the second slurry in which the electroconductivematerial and the polymer are dispersed in the non-aqueous solvent, isapplied onto the current collector, and the applied slurry is dried. Touniformly apply the second slurry, the solid content concentration ofthe second slurry containing at least the electroconductive material andthe polymer, may be from 13 mass % to 35 mass %.

The thickness of the layer corresponding to the part formed by applyingand drying the second slurry (hereinafter, the layer may be referred toas “second coating layer”) is not particularly limited. The thicknessmay be from about 1 μm to about 10 μm, or it may be from about 2 μm toabout 6 μm. The thickness of the second coating layer is obtained from,for example, a difference between the thickness of the laminate beforethe second coating layer is formed and the thickness of the laminateafter the second coating layer is formed.

In general, after the second slurry is applied and dried, the firstcoating layer and the solid content of the second slurry are combined toform the PTC resistor layer.

Before laminating the electrode active material layer on the PTCresistor layer, the laminate of the current collector and the PTCresistor layer may be pressed. The laminate may be pressed by rollpressing, cold isostatic pressing (CIP), hot isostatic pressing (HIP),etc. When the applied pressing pressure is too high, the PTC resistorlayer may be cracked. For example, in the case of roll pressing, thepressing pressure may be a line pressure of from 5.6 kN/cm to 22.4kN/cm.

By pressing the laminate of the current collector and the PTC resistorlayer, the porosity of the PTC resistor layer can be controlled to 5% to13% (see Examples 1 to 3).

(b) Laminating the Electrode Active Material Layer on the PTC ResistorLayer

By laminating the electrode active material layer on the PTC resistorlayer, a laminate of the electrode active material layer, the PTCresistor layer and the current collector is produced. Details of thematerials that can be used to form the electrode active material layer(an electrode active material, a binder and a solid electrolyte) are asdescribed above.

As the method for forming the electrode active material layer, a knowntechnique may be used. For example, the electrode active material layercan be formed as follows: a mixture of raw materials for the electrodeactive material layer is stirred well; the raw material mixture isapplied onto a substrate or onto the PTC resistor layer; and the appliedraw material mixture is appropriately dried, thereby forming theelectrode active material layer.

In the case of forming the electrode active material layer on asubstrate, roll pressing in a high temperature condition (hot rollpressing) may be used. By hot roll pressing, the electrode activematerial layer thus obtained can be more densified. In the case offorming the electrode active material layer on the PTC resistor layer,if the heating temperature of the hot roll pressing is too high, thereis a possibility that the polymer in the PTC resistor layer is thermallyexpanded. Accordingly, it is needed to determine the upper limittemperature of the hot roll pressing, depending on the properties of thepolymer, the composition of the PTC resistor layer, etc. In general, thehot roll pressing may be carried out at a temperature less than themelting point of the polymer.

B. Second Embodiment

The second embodiment of the method for producing the electrode forsolid-state batteries, comprises (a) forming the first coating layer onone surface of the current collector, (b′) forming the second coatinglayer on one surface of the electrode active material layer, and (c′)producing a laminate of the current collector, the PTC resistor layerand the electrode active material layer.

Of them, (a) is the same as the first embodiment described above.Hereinafter, (b′) and (c′) will be described.

(b′) Forming the Second Coating Layer on One Surface of the ElectrodeActive Material Layer

This is a step of forming the second coating layer on the electrodeactive material layer by applying the second slurry to one surface of asubstrate, drying the applied second slurry to form the second coatinglayer, and then transferring the second coating layer from the substrateto the electrode active material layer.

In the first embodiment, as described above in (a), the second coatinglayer is formed on the first coating layer. In this step of the secondembodiment, the second coating layer is formed on the electrode activematerial layer. As just described, the two embodiments differ in themember on which the second coating layer is formed.

Transferring the second coating layer from the substrate to theelectrode active material layer, is advantageous in that the solventused in the second slurry has no influence on the electrode activematerial layer.

The second slurry and the thus-obtained second coating layer are thesame as those of the first embodiment.

The substrate used to form the second coating layer is not particularlylimited. For example, Al, PET, Cu, SUS or the like may be used.

(c′) Producing the Laminate of the Electrode Active Material Layer, thePTC Resistor Layer and the Current Collector

In this step, the current collector and the electrode active materiallayer are laminated so that the first coating layer of the currentcollector and the second coating layer of the electrode active materiallayer are in contact with each other, whereby the first coating layerand the second coating layer are combined to form the PTC resistorlayer. As a result, the laminate of the electrode active material layer,the PTC resistor layer and the current collector is formed.

(5) Measurement of the Electronic Resistance of the Electrode forSolid-State Batteries

An evaluation item of the electrode for solid-state batteries iselectronic resistance measurement. For the electronic resistancemeasurement, a solid-state battery comprising the electrode forsolid-state batteries or an evaluation sample comprising the electrodefor solid-state batteries, is used.

Hereinafter, the evaluation sample will be described. FIG. 3 is aschematic cross-sectional view of an evaluation sample including theelectrode for solid-state batteries according to the disclosedembodiments. An electrode 10 for solid-state batteries shown in FIG. 3corresponds to the electrode 10 for solid-state batteries shown in FIG.1 and to an electrode 10 for solid-state batteries shown in FIG. 2.

As shown in FIG. 3, the layer structure of an evaluation sample 50 is asfollows: current collector 3/PTC resistor layer 1/cathode activematerial layer 2/current collector 3′/cathode active material layer2/PTC resistor layer 1/current collector 3. As is clear from FIG. 3, theevaluation sample 50 is formed by disposing the current collector 3′between the cathode active material layers 2 of the two electrodes 10for solid-state batteries, the layers facing each other.

An example of the method for producing the evaluation sample is asfollows. First, two laminates of the PTC resistor layer and the currentcollector (hereinafter, each laminate may be referred to as laminate A)and two laminates of the cathode active material layer and the currentcollector (hereinafter, each laminate may be referred to as laminate B)were produced. Next, the two laminates B are laminated so that thecathode active material layer of one laminate B and the currentcollector of the other laminate B are in contact with each other. From alaminate thus obtained, the current collector disposed outside is peeledoff, thereby producing a laminate having the following layer structure:cathode active material layer/current collector/cathode active materiallayer (hereinafter, the laminate may be referred to as laminate C). Thelaminate C corresponds to the central part (cathode active materiallayer 2/current collector 3′/cathode active material layer 2) of theevaluation sample 50 shown in FIG. 3. Finally, the two laminates A arelaminated on both surfaces of the laminate C so that the cathode activematerial layers are in contact with the PTC resistor layers, therebyproducing the evaluation sample 50 shown in FIG. 3.

FIG. 3 is a schematic view of a circuit for electronic resistancemeasurement, which includes an evaluation sample. As shown in FIG. 3, atester 40 is connected to the evaluation sample 50, thereby producing acircuit 200 for electronic resistance measurement. The electronicresistance of the evaluation sample 50 in a room temperature condition(e.g., 25° C.) and the electronic resistance thereof in a hightemperature condition (e.g., 250° C.) can be measured by use of thecircuit 200 for electronic resistance measurement.

In place of the evaluation sample 50 shown in FIG. 3, a solid-statebattery described below may be used for the electronic resistancemeasurement.

FIG. 4 is a view showing a relationship between the electronicresistance of an evaluation sample including a PTC resistor layer andthe resistance of a solid-state battery comprising an electrodeincluding the PTC resistor layer. FIG. is a graph with the resistance(Ω·cm²) of the solid-state battery on the vertical axis and theelectronic resistance (Ω·cm²) of the evaluation sample on the horizontalaxis.

As is clear from FIG. 4, the resistance of the solid-state batteryincreases as the electronic resistance of the evaluation sampleincreases. As just described, since the electronic resistance of theevaluation sample and the resistance of the solid-state battery arehighly correlated with each other, the result of the electronicresistance measurement of the evaluation sample can be said to be a testresult reflecting the performance of the solid-state battery itself.

2. Solid-State Battery

The solid-state battery of the disclosed embodiments is a solid-statebattery comprising a cathode, an anode and an electrolyte layer disposedbetween the cathode and the anode, wherein at least one of the cathodeand the anode is the above-mentioned electrode for solid-statebatteries.

In the disclosed embodiments, the solid-state battery means a batterycontaining a solid electrolyte. Accordingly, as long as the solid-statebattery of the disclosed embodiments contains a solid electrolyte, thesolid-state battery may be fully composed of a solid component, or itmay contain both a solid component and a liquid component.

FIG. 2 is a view showing an example of the layer structure of thesolid-state battery of the disclosed embodiments, and it is also aschematic cross sectional view of the solid-state battery along thelaminating direction. As shown in FIG. 2, a solid-state battery 100comprises the electrode 10 for solid-state batteries, an oppositeelectrode 30, and an electrolyte layer 20 disposed between the electrode10 for solid-state batteries and the opposite electrode 30.

The electrode 10 for solid-state batteries corresponds to theabove-described electrode for solid-state batteries according to thedisclosed embodiments. The opposite electrode is an electrode facing theelectrode 10 for solid-state batteries. The electrode 10 for solid-statebatteries and the opposite electrode 30 may be the cathode and theanode, respectively; the electrode 10 for solid-state batteries and theopposite electrode 30 may be the anode and the cathode, respectively;or, unlike FIG. 2, each of the cathode and the anode may be theelectrode for solid-state batteries according to the disclosedembodiments.

The electrode 10 for solid-state batteries is as described above. Theopposite electrode 30, that is, a cathode or anode that is generallyused in the solid-state battery, may be selected from known techniques.Especially, the cathode active material layer and cathode currentcollector which can be used in the cathode, and the anode activematerial layer and anode current collector which can be used in theanode, may be appropriately selected from the above-described materialsused in the disclosed embodiments.

The electrolyte layer 20 is not particularly limited, as long as it is alayer having ion conductivity. The electrolyte layer 20 may be a layercomposed of a solid electrolyte only, or it may be a layer containingboth a solid electrolyte and a liquid electrolyte.

As the electrolyte layer composed of the solid electrolyte only,examples include, but are not limited to, a polymer solid electrolytelayer, an oxide solid electrolyte layer and a sulfide solid electrolytelayer.

As the electrolyte layer containing both the solid electrolyte and theliquid electrolyte, examples include, but are not limited to, a poroussolid electrolyte layer impregnated with an aqueous or non-aqueouselectrolyte solution.

The form of the solid-state battery of the disclosed embodiments is notparticularly limited. As the form of the solid-state battery, examplesinclude, but are not limited to, common forms such as a coin form, aflat plate form and a cylindrical form.

The solid-state battery of the disclosed embodiments may be a singlecell as shown in FIG. 2, or it may be an assembly of the single cells.As the cell assembly, examples include, but are not limited to, a cellstack composed of a stack of single cells in a flat plate form.

As described above, in the pressure-applied condition, the electrode forsolid-state batteries according to the disclosed embodiments exerts theexcellent effect of suppressing a decrease in solid-state batteryperformance. Accordingly, the electrode for solid-state batteriesaccording to the disclosed embodiments exerts the excellent effect evenwhen an unintentional pressure is applied (such as occurrence of afailure in the solid-state battery due to an internal short circuit,overcharging, etc.) or even when an intentional pressure is applied(such as use of a confining member in combination with the solid-statebattery). In general, a failure occurs in the solid-state battery whenan unexpected local pressure is applied to the solid-state battery.Also, in the case of using the confining member in combination with thesolid-state battery, a predetermined pressure is generally applied tothe whole solid-state battery.

The confining member may be a member that can apply a confining pressureto the laminate of the two electrodes and the electrolyte layer disposedtherebetween, in the approximately parallel direction to the laminatingdirection. A known solid-state battery confining member may be used incombination with the solid-state battery of the disclosed embodiments.As the known solid-state battery confining member, examples include, butare not limited to, a confining member comprising a pair of plates thatare used to sandwich the solid-state battery, one or more rods that areused to connect the two plates, and a controller that is connected tothe rod(s) and used to control the confining pressure by use of a screwstructure, etc. In this case, the confining pressure applied to thesolid-state battery can be controlled by appropriately controlling thecontroller.

The confining pressure is not particularly limited. It may be 0.1 MPa ormore, may be 1 MPa or more, or may be 5 MPa or more. When the confiningpressure is 0.1 MPa or more, the layers constituting the solid-statebattery are in better contact with each other. On the other hand, theconfining pressure may be 100 MPa or less, may be 50 MPa or less, or maybe 20 MPa or less, for example. When the confining pressure is 100 MPaor less, it is not needed to use the special confining member.

EXAMPLES

Hereinafter, the disclosed embodiments will be further clarified by thefollowing examples. The disclosed embodiments are not limited to thefollowing examples, however.

1. Production of an Evaluation Sample Example 1

(1) Production of a Laminate of a PTC Resistor Layer and an AluminumFoil

The following materials for a first slurry were prepared.

-   -   Electroconductive material: Furnace black (manufactured by:        Tokai Carbon Co., Ltd., average primary particle diameter: 66        nm)    -   Insulating inorganic substance: Alumina (product name: CB-P02,        manufactured by: Showa Denko K. K., average particle diameter        (D₅₀): 2 μm)    -   Polymer: PVDF (product name: KF POLYMER L #9130, manufactured        by: Kureha Corporation)    -   Non-aqueous solvent: N-methylpyrrolidone

The furnace black, the PVDF and the alumina were mixed at a volume ratioof 10:30:60 to prepare a mixture. The N-methylpyrrolidone was added tothe mixture, thereby producing the first slurry. Then, the first slurrywas applied on an aluminum foil having a thickness of 15 μm (a currentcollector). The applied first slurry was dried in a stationary dryingoven at 100° C. for one hour, thereby forming a PTC resistor layerhaving a thickness of 10 μm.

The above step was carried out twice to produce two laminates of the PTCresistor layer and the aluminum foil (laminates A). The laminates A weresubjected to roll pressing under the conditions of a line pressure of5.6 kN/cm and room temperature.

(2) Production of a Laminate of a Cathode Active Material Layer and anAluminum Foil

The following materials for the cathode active material layer were putin a container to obtain a mixture.

-   -   Cathode active material: LiNi_(1/3)Co_(1/3)O₂ particles (average        particle diameter: 6 μm)    -   Sulfide-based solid electrolyte: Li₂S—P₂S₅-based glass ceramic        particles containing LiI and LiBr (average particle diameter:        0.8 μm)    -   Electroconductive material: VGCF    -   Binder: A 5 mass % solution of a PVDF-based binder in butyl        butyrate

The mixture in the container was stirred by an ultrasonic disperser(product name: UH-50, manufactured by: SMT Co., Ltd.) for 30 seconds.Next, the container was shaken by a shaking device (product name: TTM-1,manufactured by: Sibata Scientific Technology Ltd.) for three minutes.The mixture in the container was further stirred by the ultrasonicdisperser for 30 seconds, thereby preparing a slurry for forming thecathode active material layer.

Using an applicator, the slurry for forming the cathode active materiallayer was applied to one surface of an aluminum foil (serving as acathode current collector, manufactured by Showa Denko K. K.) by thedoctor blade method. The applied slurry was dried on a hot plate at 100°C. for 30 minutes, thereby forming the cathode active material layer onone surface of the aluminum foil.

The above step was carried out twice to produce two laminates of thecathode active material layer and the aluminum foil (laminates B).

(3) Production of an Evaluation Sample

First, a laminate C was produced by use of the two laminates B. Thelaminate C had the following layer structure: cathode active materiallayer/aluminum foil/cathode active material layer. Details are asfollows.

The two laminates B were laminated so that the cathode active materiallayer of one laminate B and the aluminum foil of the other laminate Bwere in contact with each other. A laminate thus obtained was subjectedto roll pressing at 10 kN/cm in a room temperature condition, therebyobtaining a laminate having the following layer structure: cathodeactive material layer/aluminum foil/cathode active materiallayer/aluminum foil. The aluminum foil disposed outside the laminate waspeeled off from the laminate. The laminate was subjected to rollpressing at 50 kN/cm at 165° C. to densify the two cathode activematerial layers, thereby obtaining a laminate having the following layerstructure: cathode active material layer/aluminum foil/cathode activematerial layer (the laminate C).

The laminate C was disposed between the laminates A and they werelaminated so that the cathode active material layers of the laminate Cwere in contact with the PTC resistor layers of the laminates A, therebyobtaining the evaluation sample of Example 1 having the following layerstructure: aluminum foil/PTC resistor layer/cathode active materiallayer/aluminum foil/cathode active material layer/PTC resistorlayer/aluminum foil.

A cross section of the evaluation sample of Example 1 was the same asthe evaluation sample 50 shown in FIG. 3. As shown in FIG. 3, the layerstructure of the evaluation sample was as follows: current collector 3(aluminum foil)/PTC resistor layer 1/cathode active material layer2/current collector 3′ (aluminum foil)/cathode active material layer2/PTC resistor layer 1/current collector 3 (aluminum foil). As is clearfrom FIG. 3, the evaluation sample 50 was formed by disposing thecurrent collector 3′ (aluminum foil) between the two electrodes 10 forsolid-state batteries.

Example 2

The evaluation sample of Example 2 was produced in the same manner asExample 1, except that in “(1) Production of a laminate of a PTCresistor layer and an aluminum foil”, the roll pressing pressure appliedto the laminates A was changed from 5.6 kN/cm to 14.2 kN/cm.

Example 3

The evaluation sample of Example 3 was produced in the same manner asExample 1, except that in “(1) Production of a laminate of a PTCresistor layer and an aluminum foil”, the roll pressing pressure appliedto the laminates A was changed from 5.6 kN/cm to 22.4 kN/cm.

Comparative Example 1

The evaluation sample of Comparative Example 1 was produced in the samemanner as Example 1, except that in “(1) Production of a laminate of aPTC resistor layer and an aluminum foil”, the laminates A were notsubjected to roll pressing.

2. Evaluation of the Evaluation Samples

The evaluation samples of Examples 1 to 3 and Comparative Example 1 wereevaluated as follows. The results are shown in Table 1.

(1) Calculation of Porosity

For the laminates A used to produce the evaluation samples (thelaminates of the PTC resistor layer and the aluminum foil) and for analuminum foil that is the same type as the aluminum foil used to producethe laminates A, the mass and the thickness were measured as follows,and then the density was also calculated as follows.

a. Mass

The laminate A and the aluminum foil were each cut into an area of 1cm². The mass m₁ of the cut laminate A and the mass m₀ of the cutaluminum foil were measured by use of an analytical balance (productname: GR-202, manufactured by: A&D Co., Ltd.)

b. Thickness

The thickness t₁ of the cut laminate A and the thickness t₀ of the cutaluminum foil were measured by use of a thickness gauge (product name:PG-01J, manufactured by: Teclock Corporation, probe: ZS-579).

c. Density

The density d (g/cm³) of the PTC resistor layer was obtained by thefollowing formula (x), using the true densities (g/cm³) of the followingthree materials used to form the PTC resistor layer and the volumeratios (%) of the materials in the PTC resistor layer.

-   -   Furnace black (manufactured by: Tokai Carbon Co., Ltd., average        primary particle diameter: 66 nm)    -   Alumina (product name: CB-P02, manufactured by: Showa Denko K.        K., average particle diameter (D₅₀): 2 μm)    -   PVDF (product name: KF POLYMER L #9130, manufactured by: Kureha        Corporation)        d=(td ₁ ×v ₁ +td ₂ ×v ₂ +td ₃ ×v ₃)/100  Formula (x)        where d is the density (g/cm³) of the PTC resistor layer; td₁ is        the true density (g/cm³) of the furnace black; v₁ is the volume        ratio (%) of the furnace black; td₂ is the true density (g/cm³)        of the alumina; v₂ is the volume ratio (%) of the alumina; td₃        is the true density (g/cm³) of the PVDF; and v₃ is the volume        ratio (%) of the PVDF.

d. Porosity

The porosity p (%) of the PTC resistor layer of each evaluation samplewas calculated by the following formula (y), using the above-obtainedthickness, mass and density values.p=[(m ₁ −m ₀)/{(t ₁ −t ₀)×1 cm² ×d}]×100  Formula (y)where p is the porosity (%) of the PTC resistor layer; m₁ is the mass(g) of the laminate A; m₀ is the mass (g) of the aluminum foil; t₁ isthe thickness (cm) of the laminate A; t₀ is the thickness (cm) of thealuminum foil; and d is the density (g/cm³) of the PTC resistor layer.

(2) Measurement of the Electronic Resistance

As shown in FIG. 3, a tester (“40” in FIG. 3, product name: RM3545,manufactured by: Hioki E.E. Corporation) was connected to the evaluationsample 50, thereby producing the circuit 200 for electronic resistancemeasurement. The electronic resistance of the evaluation sample 50 in aroom temperature (25° C.) condition was measured by use of the circuit200 for electronic resistance measurement.

The following Table 1 is a table comparing the roll pressing pressures,porosities and electronic resistances of the evaluation samples ofExamples 1 to 3 and Comparative Example 1.

TABLE 1 Roll pressing Electronic pressure Porosity resistance (kN/cm)(%) (%) Example 1 5.6 13 54 Example 2 14.2 5 29 Example 3 22.4 5 33Comparative — 33 100 Example 1

3. Conclusion

According to Table 1, the porosity of Comparative Example 1 is 33% andhigh. This result means that for the evaluation sample of ComparativeExample 1, the inside of the PTC resistor layer is relatively sparseand, as a result, the number of electron-conductive paths inside the PTCresistor layer is small.

The porosities of Examples 1 to 3 are from 5% to 13% each. These resultsmeans that for the evaluation samples of Examples 1 to 3, the inside ofthe PTC resistor layer is relatively dense and, as a result, manyelectron-conductive paths are contained inside the PTC resistor layer.

According to Table 1, each of the electronic resistance values ofExamples 1 to 3 in a room temperature condition, is 29% to 54% of theelectronic resistance value of Comparative Example 1 in a roomtemperature condition.

Accordingly, since the porosity of the PTC resistor layer is in thespecific value range, more electron-conductive paths than ever beforeare contained inside the PTC resistor layer, and excellent electronconductivity inside the PTC resistor layer is obtained. As a result, itwas proved that when the electrode is used in a solid-state battery, anincrease in the electronic resistance inside the PTC resistor layer issuppressed, and a decrease in the performance of the solid-state batteryis suppressed.

As described above, the results of the electronic resistance measurementof the evaluation samples can be said to be test results reflecting theperformance of the solid-state battery itself (FIG. 4).

REFERENCE SIGNS LIST

-   1. PTC resistor layer-   2. Electrode active material layer-   3, 3′. Current collector-   10. Electrode for solid-state batteries-   20. Electrolyte layer-   30. Opposite electrode-   40. Tester-   50. Evaluation sample-   100. Solid-state battery-   200. Circuit for electronic resistance measurement

The invention claimed is:
 1. An electrode for solid-state batteries,wherein the electrode comprises an electrode active material layer, acurrent collector and a PTC resistor layer disposed between theelectrode active material layer and the current collector; wherein thePTC resistor layer contains an electroconductive material, an insulatinginorganic substance and a polymer; wherein a porosity of the PTCresistor layer is from 5% to 13%; wherein the PTC resistor layercontains at least a first coating layer and a second coating layer;wherein the second coating layer is disposed between the first coatinglayer and the electrode active material layer; and wherein the secondcoating layer does not contain the insulating inorganic substance. 2.The electrode for solid-state batteries according to claim 1, whereinthe insulating inorganic substance is a metal oxide.
 3. The electrodefor solid-state batteries according to claim 1, wherein theelectroconductive material is carbon black.
 4. A solid-state batterycomprising a cathode, an anode and an electrolyte layer disposed betweenthe cathode and the anode, wherein at least one of the cathode and theanode is the electrode for solid-state batteries defined by claim 1 . 5.The electrode for solid-state batteries according to claim 1, whereinthe thickness of the second coating layer is from 1 μm to 10 μm.
 6. Theelectrode for solid-state batteries according to claim 1, wherein theaverage particle diameter (D50) of the insulating inorganic substance isfrom 0.2 μm to 5 μm.